The National Security Agency gathered records of Americans' mobile phone call locations to test how it could process the data in bulk, but abandoned the plan, senators are told.

WASHINGTON — The National Security Agency collected samples of records showing where Americans were when they made mobile phone calls in 2010 and 2011 to test how it could obtain and process the data in bulk, but decided not to move forward with the plan, intelligence officials disclosed Wednesday.

The admission by NSA chief Keith Alexander to a Senate committee solved part of a mystery about the digital spying agency's involvement with data that could reveal the day-to-day movements of — and deeply personal information about — every cellphone user.

Spurred by leaks from former contractor Edward Snowden, the NSA has admitted it collects in bulk the "to and from" calling records of Americans, but has denied collecting the location information that attaches to each mobile phone call.It is now clear the agency considered doing that.

The test-run data were "never available for intelligence analysis purposes," Alexander said, and in June, the NSA promised to notify Congress before any further locational data were collected.

"I would just say that this may be something that is a future requirement for the country, but it is not right now," Alexander said. The FBI can get location data on suspects through court-approved, case-specific warrants, he said.

Sen. Ron Wyden (D-Ore.), who receives classified briefings as a member of the Senate Intelligence Committee, had been pressing the NSA to acknowledge its flirtation with bulk collection of U.S. location data. He said in a statement there was more to the story, but did not elaborate.

"After years of stonewalling on whether the government has ever tracked or planned to track the location of law-abiding Americans through their cellphones, once again, the intelligence leadership has decided to leave most of the real story secret — even when the truth would not compromise national security," Wyden said.

In the U.S., mobile phone location information is commonly used in criminal investigations and civil lawsuits after being obtained through search warrants or other legal demands. It is also sold in bulk — with no user names attached — by mobile phone companies to other companies that mine the data for marketing purposes.

Privacy activists fear that bulk collection of the data could subject people to invasion of privacy by disclosing political gatherings, illicit affairs, trips to therapists and other personal information.

The NSA already vacuums up as much mobile phone location data on foreign targets outside the U.S. as it can get, former officials say.

The news of the NSA's location data test emerged at a Senate Judiciary Committee hearing on agency surveillance as the director of national intelligence, James R. Clapper, offered a new rationale for the agency's controversial collection of U.S. calling records in bulk.

Under the supervision of the Foreign Intelligence Surveillance Court, the NSA since 2007 has built a database of so-called telephony metadata that includes calls made by nearly every American. The data include records of calls for each telephone number, but not names, addresses or the contents of any communication, officials have said.

Intelligence agencies query the database when they identify specific phone numbers that are believed to be linked to terrorist groups. Last year, 300 phone numbers were run through the database, officials have said.

Intelligence officials have publicly identified only a single terrorism financing case in the U.S. that was cracked because of that program, and a second case in which it played a central role. Senate Judiciary Committee Chairman Patrick J. Leahy (D-Vt.) pressed Clapper and Alexander on that point.

"We have heard over and over again the assertion that 54 terrorist plots were thwarted by the use of Section 215 and/or Section 702 authorities," Leahy said, referring to parts of surveillance law. "That's plainly wrong, but we still get it in letters to members of Congress; we get it in statements. These weren't all plots, and they weren't all thwarted. The American people are getting left with an inaccurate impression of the effectiveness of NSA programs."

Alexander acknowledged that only in two cases at most could officials say that domestic terrorist activity would not have been detected without the collection of American phone records.

But Clapper added that determining "plots foiled" was not the only way to measure the usefulness of the domestic phone database. The records also allow analysts to rule out domestic conspiracies, he said.

"I would call it the 'peace of mind' metric," he said. He said that after April's Boston Marathon bombings, officials used the database "to check out whether there was or was not a subsequent plot involving New York City."

No co-conspirators were found.

And this summer, when a threat from Al Qaeda's Yemen affiliate forced the closure of diplomatic facilities across the Middle East, Clapper said, analysts were able to run terrorist phone numbers against American records, and take comfort in the fact that no connection turned up.

Clapper also lamented the effect of the government shutdown on the intelligence community, saying it made employees more vulnerable to recruitment by a foreign intelligence agency to spy on the United States.

Leahy was not convinced.

"The government has not made its case that bulk collection of domestic phone records is an effective counter-terrorism tool, especially in light of the intrusion on American privacy," he said.

Other lawmakers support the program, however, and legislation to curb it faces an uncertain future.